Are Portland ADU rules different from DADU rules?

Yes, Portland treats ADUs and DADUs as distinct categories with different cost profiles, even though both are now broadly allowed on residentially zoned lots after the Residential Infill Project (RIP) and Oregon HB 2001 / SB 1051 liberalization.

An ADU is any accessory dwelling unit attached to or carved out of the primary residence, including basement conversions, attic conversions, and attached additions over an existing garage. A DADU is a detached accessory dwelling unit on the same lot, typically a freestanding cottage or a unit built above a detached garage. Both categories are governed by Portland Zoning Code Title 33 and reviewed by the Bureau of Development Services through the standard residential permit track.

The cost gap is structural, not regulatory. Attached ADUs reuse existing foundation, walls, and often roof structure, which is why budgets typically run between 95,000 and 225,000 dollars in Portland. DADUs require new foundation, new utility runs (water, sewer, electrical, often gas), new envelope, and new roof, pushing budgets to 180,000 to 400,000 dollars depending on size and finish level.

Homeowner decisions usually come down to four questions. Do you have basement headroom or daylight that supports a livable conversion? Do you have rear-yard area that meets setback minimums (5 feet side and rear in most R-zones)? Do you want owner-occupancy flexibility, since DADUs often command higher rent? And what is your sewer-line condition, since DADUs frequently require a sewer-line capacity upgrade or a separate lateral.

The most common gotcha is assuming you can convert a non-conforming garage in place without addressing setback, roof pitch, or foundation deficiencies. The second is underestimating Portland Water Bureau and BES connection fees, which can add 15,000 to 30,000 dollars to a DADU.

Baily can route you to GCs whose recent portfolios skew ADU or DADU and can pull realistic comparables for your lot. Start a chat with your address and rough scope.